1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic image forming process and, more particularly, to an image forming apparatus and a method for controlling the image forming apparatus which includes a developer amount detector for successively detecting the remaining amount of developer in a developer container.
2. Description of the Related Art
Image forming apparatuses form an image on a recording medium using an electrophotographic process. The image forming apparatuses include an electrophographic copying machine, electrophotographic printer (such as an LED printer, and laser beam printer), electrophotographic facsimile device, and electrophotographic word processor.
A developing device may be a process cartridge into which a photoconductive structure as an image bearing body, a developing unit for supplying a developer to the photoconductive structure, and a cleaning unit for cleaning the photoconductive structure are integrated. The process cartridge is detachably mounted on the image forming apparatus. Alternatively, at least both a development unit and a developer container may be integrated into a development cartridge, which is detachably mounted on the image forming apparatus.
In the image forming apparatus using an electrophotographic process, light responsive to image information is directed to a photoconductive structure as an image bearing body to form a latent image. The development unit feeds a developer as a recording material to the latent image to develop a developer image. The developer image is then transferred to a recording medium. An image is thus formed on the recording medium.
The image forming apparatus of this type employs a process cartridge into which at least both a photoconductive structure and a development unit are integrated. The process cartridge is detachably mounted on the image forming apparatus. Since the user himself performs maintenance in this type of the image forming apparatus, operability of the apparatus is substantially improved. The process cartridge method is this widely used in the electrophotographic image forming apparatuses.
The developer contained in the developer container in the cartridge is consumed as the image forming apparatus forms images. When the developer is fully consumed, the user replaces the cartridge with a new cartridge to start over. It is necessary to let the user know regularly how much developer has been consumed and how much developer remains. Many image forming apparatuses are provided with a developer amount detector in the process cartridge thereof. The developer amount detector regularly detects the amount of developer to urge the user to prepare a new cartridge before an expected cartridge replacement time for appropriate and efficient cartridge replacement.
The developer amount detector disclosed in Japanese Patent Laid-open No. 2001-290354 proposes a developer amount detector. The developer amount detector includes two electrodes facing a developer bearing structure and a bottom surface of a developer container. A variation in a capacitance between each of the two electrodes and the developer bearing structure is detected. The developer amount detector detects the amount of developer within the developer container, and lets the user know the use status of the developer.
The method of detecting the remaining amount of developer by measuring a capacitance between a plurality of electrodes and a developer bearing structure in the conventional developer amount detector having the above-referenced construction requires a relatively simple circuit and results in fairly accurate measurements. For this reason, a variety of developer amount detectors have been proposed. The conventional developer amount detector includes the two electrodes to cover a wide detection range of developer. The distance between each electrode and the developer bearing structure becomes far depending on the construction of the developer container if the volume of the developer within the cartridge is increased. When the capacitance between the electrode and developer bearing structure is measured, the detected capacitance is more subject to noise. If the electrode is influenced by external noise (in the form of electromagnetic interference generated in other electronics), or if no correct voltage is applied to the electrode (antenna) in the cartridge as a result of a foreign matter (such as staples) introduced into the apparatus, no correct detected value is obtained. The conventional developer amount detector detects an erroneous developer amount.